Cucurbit[7]uril: a high-affinity host for encapsulation of amino saccharides and supramolecular stabilization of their α-anomers in water.

Cucurbit[7]uril (CB[7]), an uncharged and water-soluble macrocyclic host, binds protonated amino saccharides (D-glucosamine, D-galactosamine, D-mannosamine and 6-amino-6-deoxy-D-glucose) with excellent affinity (Ka=103 to 104 M−1). The host–guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI-TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D-mannosamine, are bound as α-anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D-galactosamine hydrochloride (Ka=1.6×104 M−1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α-anomer by the host.